Life has been found in some very unexpected places on Earth. In deep caves, in ice cores, and at the deepest depths of the oceans. An interesting question; is there a temperature below which life cannot exist?

A new study, published in PLoS One, reveals that below -20 °C, single-celled organisms dehydrate, sending them into a vitrified — glass-like — state during which they are unable to complete their life cycle.

The researchers propose that, since the organisms cannot reproduce below this temperature, -20 °C is the lowest temperature limit for life on Earth.

Scientists placed single-celled organisms in a watery medium, and lowered the temperature. As the temperature fell, the medium started to turn into ice and as the ice crystals grew, the water inside the organisms seeped out to form more ice. This left the cells first dehydrated, and then vitrified. Once a cell has vitrified, scientists no longer consider it living as it cannot reproduce, but cells can be brought back to life when temperatures rise again. This vitrification phase is similar to the state plant seeds enter when they dry out.

'The interesting thing about vitrification is that in general a cell will survive, where it wouldn't survive freezing, if you freeze internally you die. But if you can do a controlled vitrification you can survive,' says Professor Andrew Clarke of NERC's British Antarctic Survey , lead author of the study. 'Once a cell is vitrified it can continue to survive right down to incredibly low temperatures. It just can't do much until it warms up.'